METHOD FOR FABRICATING AN EJECTOR TUBE FOR MOULDS

Abstract: The method for obtaining expulsion tubulars where are guided the corresponding expellers used in moulds, for example injection moulds, comprises a series of operations which are carried out on a tube (1), the first operation consisting in cutting a portion of the tube (1) to the desired length, with an excess of diameter to allow for an eventual grinding. In a second phase, a reduction of diameter is carried out in an extreme region (2), in order to proceed, in a third phase, to an external pre-grinding (3), the fourth phase consisting in an internal machining of the extreme region (2) with a total concentricity. In the fifth phase, an inductive tempering is effected, and continuously, in a sixth phase, an external grinding is performed in order to obtain the desired external diameter, the seventh phase consisting in an internal grinding on the internal diameter of the area (2), and finally the eighth phase consists in a frontal facing (6), thereby obtaining an expulsion tubular (1) for moulds, in general. Optionally, a swaged head may be obtained at the posterior extremity of the tubular (1).

Description: SUBJECT OF THE INVENTION The invention relates to a procedure for making an ejector tube for moulds in general, though it is intended for application in particular with injection moulds, the procedure being based on a series of stages of work carried out on a length of tubing of suitable length and diameter, this tubing being the starting point in achieving, through the minimum number of operations, the shaping of the ejector tube which serves as the guide for the ejectors used in moulds, with both the ejector tube and the ejector being held in place by a fixing head. PRIOR ART The ejector tubes used as guides for ejectors linked to their fixing heads and included in injection moulds are conventionally produced from a bar or rod which is subjected to a series of processes: first, one of the ends is worked to produce the head, which is oversized with respect to the rest of the body; next, an axial bore is cut all the way through, and then suitably machined to give two diameters; it is then trued, and further operations such as heat treatment and subsequent truing are performed until the ejector tube sought is obtained. As stated, in producing the ejector tube in the conventional manner, the starting point is a solid bar which, since its bore has to be drilled out, entails a loss of material, and furthermore this bar initially is very heavy. For example, to produce a standard ejector tube measuring 400 mm in length with a bore diameter of 8 mm and an outside diameter of 12 mm, the starting point is a bar of metal whose total weight is approximately 1,290 grams. Furthermore, special machine tools are needed to produce it. As a consequence of all this, fourteen to sixteen different operations have to be performed - a long and laborious process. It must also be borne in mind that, since material has to be removed to produce the bore, molecules will be broken, thereby reducing elasticity in the mechanical strength of the end product. Another physical problem which cannot be eliminated arises during the heat treatment, since the various molecular masses which make up the product have varying thicknesses, and this makes the cooling stage in the hardening fragile, plastic deformations arising which require a special, additional truing process. Finally, it must be pointed out that, in conventionally produced ejector tubes, when the tube has to be cut to length, the cut has to be made at the upper end, since naturally this operation is performed after attaching the piece to the appropriate fixing head; since this area of the piece is the one in which the ejector and the tube itself are close-fitted, and since the cutting reduces the size of this area, that close-fit quality is lost. JP-A-4 235 203 describes a manufacturing process for making an ejector tube comprising the steps of producing a hollow rod-formed extrusion moulded product, sintering this product, and machining the product to form the shape of the ejector tube. Thereby, the step of drilling the axial bore is eliminated. DESCRIPTION OF THE INVENTION The procedure advanced was designed to resolve these problems fully by starting from a length of tubing, which to begin with provides a considerable saving in weight, since to produce a tube of approximately the same size as the one referred to in the previous section, the weight involved in the procedure of this invention is approximately 220 grams, as against the 1,290 grams of the total weight of the piece which is the starting point for the conventional method. Secondly, the ejector tube is designed to be correctly and effectively held by means of a fixing head which was claimed as a novelty in utility model 9103746 by the same applicant. Among noteworthy advantages is the fact that no material has to be removed, and so no molecules are broken, to which must be added that the ejector tube is adjusted or cut at the lower end by virtue of its placing on the relevant fixing heads, and it can be removed from the top end of these, the lower close-fitted part being reduced. In particular, the procedure of this invention, starting from a tube of suitable length and inside and outside diameters, consists of the following operational stages: Cutting the tube to the desired length, with the inside and outside diameters slightly oversized with respect to the final diameters. Deforming one end section of the tube, from the outside in, to reduce the inside diameter of that end section. Performing a pre-truing operation outside to bring the diameter of the tube down to the desired value. Machining the inside of the deformed end section, with total concentricity. Carrying out induction hardening. Truing to achieve a desired size in the outside diameter. Truing to achieve the desired inside diameter of the deformed end section. Truing the front end of the deformed end section, with optional nitriding. A final complete check of the tube thus obtained. Preferably, the close-fit bore is lapped to achieve a final size, with optional nitriding. In this way the tube is obtained, suitable for fitting to the existing ejector bases, providing quick changing in injection moulds. In circumstances in which the moulds do not require quick tube changing, or in the case of moulds that are of less expensive design or produced in smaller batches, the procedure is to rivet on the back of the tube, finished as described above, a heat-formed butt onto the tube itself, by the stamping process, this operation being achieved by compressing onto the tube itself, re-heated by induction, on a predetermined circular structure and with a mould of the desired shape, on the basis of an impact procedure which may be interchangeable or fixed in accordance with the requirements of each case. The inside diameter will in all cases be slightly smaller than the nominal diameter required, to eliminate the relieving operation necessary in working, in order to avoid the internal ejector rubbing along all its length, since a close-fit area is only needed in accordance with the friction areas required. The ejector tube thus formed is obtained through a continuous process of heat treatment by induction, no deformations of any type arising; not only is the product concerned improved, but the onerous task of truing required in the traditional systems is eliminated. Moreover, the ejector tube will provide a number of advantages over conventional ones since, as is well known, conventional tubes are supplied in standard dimensions, each manufacturer having to adapt them to the specifications set; in every case the requirements of the product to be manufactured demand the length to be adjusted, and so the ejector tubes need to be shortened as required, which involves removing part of the friction zone, and this entails losses in the part and its friction, which significantly shortens the ejector tube's service life. The ejector tube obtained through the procedure of this invention, being a tube throughout, gives the great advantage of allowing it to be cut at the rear end for the purpose of adapting it to the required size, so preserving in all cases the entire friction zone and thus lengthening the duration of that ejector tube. Another important advantage lies in the fact that, in the event of a breakage or accident befalling the mould during the injection process, it is not necessary to remove the machine mould nor to disassemble the entire ejector unit in order to change the ejector tube, those being operations that are very time-consuming; if it proves necessary to replace the ejector tube for any reason during the injection process, all that has to be done is to open the machine, to advance the ejector bridge until it presses against the press bushing and then to remove the damaged or defective ejector tube replacing it with another one and cutting off the excess length at the rear to the length required. Furthermore, this ejector tube produced through the procedure described is very tough, since all the fibres have a single-direction molecular structure owing to having been shaped by the drawing process, and this gives higher tensile and compression strength. DESCRIPTION OF THE DRAWINGS As a complement to the description given, and in order to assist understanding of the features of the invention, attached to this specification as an integral part hereof is a set of drawings showing, for illustrative purposes with no limitation entailed, the following: Figures 1a, 1b, 1c, 1d, 1e, 1f, 1g and 1h show in consecutive order the various stages in producing the ejector tube in accordance with the procedure that is the subject of the invention. Figures 2a and 2b show the possibility of including an intermediate stage, as will be described subsequently, to achieve a butt heat-formed on the tube itself as produced by the process shown in the previous figure. PREFERENTIAL EMBODIMENT OF THE INVENTION As can be seen in the figures referred to above, and with particular reference to figure 1a, it can be observed how the procedure of the invention takes as its starting point a length of tubing (1), cut in the procedure's first stage to the desired length, and with its inside and outside diameters slightly oversized. During the second stage, an end area (2) of the length of tubing (1) is submitted to external deformation, acting inwards, in order to reduce the inside diameter of this end length (2). In the third stage, the body or length of tubing (1) is pre-trued at the area shown as (3), to make the outside diameter the same as the final or desired truing. In the fourth stage, the length of tubing (1) is machined along the inside area or sliding area down to the desired diameter, with perfect concentricity. Next the body (1) is induction treated, and then in the next stage it is trued as shown at (4), this truing being on the outside to obtain the final diameter desired. In the next stage, internal truing is performed, as shown at (5), to achieve the inside diameter desired. Finally, in the final stage the front is trued as shown at (6), and the tube is optionally subjected to nitriding, the tube thus being obtained as desired. Between the seventh and eighth stages, i.e. between the last and the second-to-last stages, the tube (1) may be submitted to butting (7) by stamping to obtain the end form (8) shown in the second stage of this second figure. It is not deemed necessary to prolong further this description since any expert in the subject will appreciate the scope of the invention and the advantages it brings. The materials, shape, size and arrangements of the elements may all be altered provided such alteration does not go beyond the scope of the claims.

Claims: A manufacturing procedure for making an ejector tube for moulds which, taking a length of a tube (1) as the starting point, consists of the following operating stages: cutting the tube (1) to the desired length, with the inside and outside diameters slightly oversized with respect to the final diameters; deforming one end section (2) of the tube (1), from the outside in, to reduce the inside diameter of that end section (2); pre-truing of the outside (3) to bring the diameter of the tube (1) down to the desired value; machining the inside of the deformed end section (2), ensuring total concentricity; treating the tube (1) by induction hardening; external truing (4) of the tube (1) to bring its diameter to the desired value; internal truing (5) of the diameter of the deformed end section (2) to obtain the diameter desired for this end section; truing the front end (6) of the deformed end section (2), with optional nitriding; and a final complete check of the tube thus obtained. A manufacturing procedure for making an ejector tube for moulds, as in claim 1, characterized in that optionally, between the seventh and eighth stages of the previous claim, a butt (7) may be heat-formed on the rear end of the tube (1), this operation being performed by compression, with the tube heated by induction, to obtain a pre-established circular shape (8) by means of a mould of the appropriate shape.

Inventors: NAVARRA PRUNA ALBERTO, NAVARRA PRUNA, ALBERTO
Applicants: NAVARRA PRUNA ALBERTO, NAVARRA PRUNA, ALBERTO
Application year: 1994
Main classification: B23P15
IPC codes: B23P15, B23P13, B29C45